That's a good question because it goes to the point about why we have written this software.

Currently, powerDns's pipe backend is more designed as a "connection" to a program that could allow getting resolution information, than a way to connect to a program that implements resolution policy.

This means that powerDns design is more focused to allow resolving certain zones for a particular domain, and in that context, pipe backend may allow accessing to that information.

However, ext-Dns server is more designed not only with that target, but to allow the posibility to ask the server to "forward" the request because "you don't oppose to that resolution" (see ext-DnsD Introduction: how it works, basic description for more details about this).

This way ext-Dns becomes more a policy-caching-forward DNS server than a zone domain server like powerDns does.

Knowing this, we wrote ext-Dns becase we wanted to have a DNS server that could allow an organization to control what is resolved and how, letting accepted requests to continue its normal DNS resolution path.